Glaucoma Conference Intraocular pressure and tonometry R3 정병주/Pf. 박찬기

Intraocular pressure

Distribution in general populations Gaussian curve with a skew toward the higher pressures

Factors affecting IOP Genetics Environment Physiology Ethnicity Sex Age Ethnicity Refractive error Diurnal and postural variation Exertional influences Eyelid and eye movement Intraocular conditions Systemic conditions

Factors affecting IOP Genetics Heredity contributes to IOP 10q22, 5q22, 14q22 Chromosomes 2, 5, 6, 7, 12, 15, and 19 But, no definite “ IOP genes”

Factors affecting IOP Environment Cold air : reduce IOP(decreased episcleral venous pressure) Reduced gravity : increase IOP(cephalad shifts) Tobacco smoking : transient increased IOP : vasoconstriction & increased episcleral venous pressure : COAG – no evidence General anesthesia : usually reduce IOP Cf) Ketamine : not reduce IOP -> EUA 시 주의를 요함 Cf) succinylcholine & suxamethonium : increase IOP -> ruptured globe & intraocular surgery 시 주의를 요함

Factors affecting IOP Environment Systemic medication : potentially affect IOP : Corticosteroid : potential risk of IOP elevation & steroid-induced glaucoma : Anticholinergic agent : AACG Acute dose of alcohol : lower IOP : combination of suppressed circulating ADH -> direct inhibition of aqueous secretion : clinically effective? -> no evidance Caffeine : slight, transient elevation : no significant , sustained pressure elevation

Factors affecting IOP Physiology Sex No major effect on IOP After menopause, apparent rise in mean IOP among women Age In children, Increase with age In Adult, Gaussian between 20 and 40 yrs, increase with advancing age Aqueous humor dynamics : Reduced facility of aqueous outflow and uveoscleral outflow : Decrease in aqueous production : Episcleral venous pressure : not change

Factors affecting IOP Ethnicity Refractive error Increased risk for COAG among blacks Increased risk for AACG among some Asians Refractive error In children, no correlation between higher IOP and myopia In adults, myopia is still a risk factor : but some studies show no association

Factors affecting IOP Diurnal and postural variation Cyclic fluctuation through the day : During the day time? : In the morning? : Before noon? Postural variation : Elevation in the night due to supine position : head-down tilt position = increased IOP due to elavated episcleral venous pressure : optic nerve damage 여부가 증명된 것은 아니지만 Yoga, Inversion 과 같은 운동은 glaucoma 환자에서 주의를 요함

Factors affecting IOP Diurnal and postural variation Adrenocortical steroid & catecholamines Circadian rhythm of aqueous humor dynamics : not related melatonin level Exertional influences Straining, electroshock, high-resistance musical instrument : Elevated episcleral venous pressure Aerobic exercise : IOP lowering effect : Maybe related to metabolic acidosis, hypocapnia, lactate

Factors affecting IOP Eyelid and eye movement : Elevate IOP Blinking : 10mmHg Hard eyelid squeezing : up to 90mmHg Voluntary eyelid fissure widening : 2mmHg Contraction of EOM

Factors affecting IOP Intraocular conditions Anterior uveitis without angle abnormality : IOP reduction : Decreased aqueous humor production Rhegmatogenous retinal detachment : IOP reduction : reduced aqueous flow : shunting of aqueous from the posterior chamber into the subretinal space

Factors affecting IOP Systemic conditions Hypertension : in some epidemiologic studies, positive correlation : combination of ocular pulse pressure and ocular perfusion pressure : retinal microvascular abnormality : not associated DM : unclear Translaminar pressure gradient across the lamina cribrosa : relatively lower CSF pressure in COAG patients Obesity & BMI : not clear

Tonometers and Tonometry

Classification of tonometers Contact tonometer : Deformation of the globe Indentation tonometers Applanation tonometers Variable force Variable area Noncontact tonometer

Classification of tonometers Indentation tonometers Truncated cone Shape : variable & unpredictable Conversion table 이 필요함(empirical) Schiöz tonometer Applanation tonometers simple flattening constant shape Mathematical calculation Goldmann tonometer Maklakoff tonometer

Classification of tonometers Applanation tonometers : differentiated on the basis of the variable Variable force Measures the force to be required to applanate(flatten) Goldman applanation tonometer Variable area Measure the area of the cornea to be flatten by a known force Maklakoff tonometer

Classification of tonometers Noncontact tonometer Use a puff of air to deform the cornea Measure the time or force to create “a standard amount of corneal deformation” Grolman

Goldmann applanation tonometry Imbert-Fick law W=Pt X A W = external force Pt= pressure in the sphere A= area flattened Perfectly spherical Dry Perfectly flexible Infinitely thin

Goldmann applanation tonometry Modified Imbert-Fick law W+S=Pt X A1 +B S = surface tension (d/t moisiture) A1 = inner area ( d/t central corneal thickness) B = a force to bend the cornea (d/t a lack of flexibility) - S=B 일 때의 원의 직경 3.06mm - 이 때 이동되는 안구 용적은 0.50 mm3 의 적은양으로 ocular ritidity는 큰 영향이 없다.

Goldmann applanation tonometry 3.06 mm

Goldmann applanation tonometry Sources of error with Goldmann tonometry amount of fluorescein : wider meniscus : falsely higher pressure Thicker cornea : falsely higher pressure Thinner cornea : falsely lower pressure : A lack of agreement on the correction factor 4D astigmatism = 1mmHg of error : 45 degrees to the major axis : An average of horizontal and vertical readings